use natrual questions model

app.py

@@ -142,7 +142,7 @@ def init_models():
     stop = set(stopwords.words('english') + list(string.punctuation))
     device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
     question_answerer = pipeline(
-        "question-answering", model='sultan/BioM-ELECTRA-Large-SQuAD2-BioASQ8B',
+        "question-answering", model='nlpconnect/roberta-base-squad2-nq',
         device=device, handle_impossible_answer=False,
     )
     reranker = CrossEncoder('cross-encoder/ms-marco-MiniLM-L-6-v2', device=device)